``Just one story,'' pleads Baby Bear, and then he'll go to sleep. When Goldie falls for what has to be the oldest line known to youngsters, ``just one'' story soon spins into a whole picture book-full. Each of the stuffed animals in Baby Bear's room--an elephant, a mole, an anteater, an alligator, a sheep and a tiger--takes a turn in the limelight as Goldie patiently makes up tales to suit her charge's fancies. The stories are pure froth, and the prolific Yolen outdoes herself at one point with an exceedingly comical account of a flock of sheep, all named Sam. Dyer, Yolen's collaborator on the Piggins books and The Three Bears Rhyme Book , treats readers to crisp, imaginatively framed images in a palette of clear, fresh colors. Ages 3-8. (Apr.)